Adams County is a county in the U.S. state of Washington. As of the 2020 census, the population was 20,613. The county seat is at Ritzville, and its largest city is Othello. The county was formed out of Whitman County in November 1883 and is named after John Adams, the second President of the United States.

Ritzville is a city in Adams County, Washington, United States. The population was 1,767 at the 2020 census. It is the county seat of Adams County. The city is part of the Othello, WA Micropolitan Area, which comprises all of Adams County, and is part of the larger Moses Lake-Othello, WA Combined Statistical Area.